1. Field of the Invention
The present invention relates in general to a variable valve system of an internal combustion engine, which is able to vary an open/close timing of engine valves (viz., intake and/or exhaust valves) in accordance with an operation condition of the engine. More specifically, the present invention relates to an improvement in reducing the size of such variable valve system.
2. Description of the Related Art
Hitherto, in the field of variable valve systems of an internal combustion engine, various types have been proposed and put into practical use. One of the systems is shown in Japanese Laid-open Patent Application (Tokkaihei) 10-8988.
The variable valve system of the published application is a device for controlling a valve timing of intake and exhaust valves in accordance with an operation condition of an associated internal combustion engine. The device comprises an intake camshaft for intake valves and an exhaust camshaft for exhaust valves.
The exhaust camshaft is provided at one end thereof with a primary sprocket around which a timing chain from a crankshaft is operatively put.
The exhaust camshaft is further provided near the primary sprocket with a secondary sprocket around which a transmission chain from a cam sprocket on the intake camshaft is operatively put.
The intake camshaft is provided at one end thereof with a valve timing control mechanism that varies a relative angular positioning between the cam sprocket and the intake camshaft with the aid of a hydraulic pressure that is fed to an oil housing body through a pressure control valve.
The oil housing body is located nearer to the exhaust camshaft than the primary sprocket of the exhaust camshaft.